The purification of water by means of ultraviolet radiation is well known. In a conventional installation, water may pass through a pre-filter and then a reverse osmosis module. Following this, the water passes through a carbon final filter, an ultraviolet irradiation unit, and then through some piping to a faucet.
While ultraviolet radiation is highly destructive to bacteria, it has been shown that under favorable circumstances, irradiated bacteria can repair themselves, given some time. Accordingly, water which has been irradiated with ultraviolet radiation may show no bacterial growth upon culturing immediately after irradiation, but later on the same water may exhibit positive results on bacteria culturing. This particularly take place by a process known as photo-reactivation, in which the bacteria are able to regain the capability to multiply in the presence of visible spectrum light.
Accordingly, even in a system such as that described above in which water passes through an ultraviolet irradiator, if the faucet is not used to draw water continuously, bacteria can revive in the portion of piping which is downstream from the irradiator, so that stagnant water in the piping downstream from the irradiator can once again become contaminated with growing bacteria, without any extra bacteria being innoculated into the stagnant water held in the faucet.
By this invention, a final ultraviolet irradiation step of very high efficiency can be provided to a faucet which carries the unit of this invention, preferably in such a manner that water cannot be stored after ultraviolet irradiation. To accomplish this, the ultraviolet unit of this invention may be designed to be at the exact end of the water flow path.
The Galtek Corporation of Chaska, Minn. discloses an ultraviolet sterilizing system in which the faucet itself through which water flows is sterilized, particularly between uses, to prevent bacteria from migrating upwardly into the faucet back toward the water source. The prime purpose of the Galtek structure is to sterilize the spout or faucet end, rather than to sterilize water passing through the faucet.
By the present invention, an ultraviolet sterilizer unit is provided, which exhibits improved efficiency for sterilizing of water, and which may be mounted on the end of the faucet to minimize or eliminate the chance that residual water which has been ultraviolet irradiated will become stagnant and reinfected with growing bacteria. The unit of this invention may be activated by turning on the faucet and deactivated by turning the faucet off, but time delay devices and the like may be provided as desired to keep the unit operating for a period of time after shut-off of the faucet.